A solar cell is referred to a device for converting a light energy into an electric energy. In the solar cell, it is important to absorb as much as solar energy in order to enhance the efficiency of the solar cell. In the event of a solar cell made of Si, GaAs, Cu2S which have a large reflection index and a solar cell formed in a M-S layer MIS structure in which an insulation film is formed on the surface of a semiconductor and a metallic layer is attached on the film, about 20˜30% of incoming light fail to generate electric charges, namely they are reflected. As a method for reducing the reflection of light, about 10% of light reflection loss can be prevented by texturing the surface in stripe patterns. In another method for reducing the reflection of light, there is an antireflection coating method in which a transparent thin film layer having an index of refraction between a semiconductor and air is made with a certain proper thickness. The silicon has 34% of light reflection loss in a longer wavelength (1.1 μm) and has 54% of light reflection loss in a shorter wavelength (0.4 μm). In the event that a transparent polymer film is made in a single layer, it is possible to reduce the reflection index by 10% in average in the above wavelength ranges.
In the method for forming a transparent polymer film, as shown in FIG. 1A, a substance having an index of refraction between a medium (air) and a substance (a glass) is coated on the surface of a glass. The lights reflected from the surface of the coating substance and the interface between the coating substance and the glass are interfered with each other and are offset when adjusting the thickness of the coating substance coated on the surface to λ/4 with respect to a specific wavelength, as a result of which the effects of the transparent polymer film can be enhanced as shown in FIG. 1B. So, it is needed to coat the substances in multiple layers for maximizing the anti reflection effects.
In the event of solar cells, a variety of researches are performed in order to enhance the efficiency. It is needed to coat a transparent polymer film on a cover a glass so that a lot of solar light can come into the interior of the solar cell. In the conventional art, a method for coating the surface of a glass is generally used. However, in the above conventional method, as the incident angle of the solar light continues to increase, the reflection of the solar light continues to increase as well, so the transmittance of the solar light is disadvantageously lowered. In recent years, a method for enhancing the effects of antireflection by forming nano size turfs in a moth eye structure comes up with a big attention.
While researching the transparent polymer film used in a solar cell, the inventors of the present invention have developed and completed a method for enhancing the transmittance of a transparent polymer film in such a manner that the nano size turfs are formed in a circular cone shape by using plasma by attaching a transparent polymer film on a glass over its large surface area.